On Thursday 12 February 2009 10:33:39 am Seth Mattinen wrote: > Just for fun I looked at my BGP mesh and found the > following: > > * Directly connected neighbors MTU=516 > * Transit to upstreams MTU=1440 or 1460 > > This is under 12.4(16) and I've never touched 'ip tcp > path-mtu-discovery' or per-neighbor MTU settings.
From our busier route reflectors (7201's), we are seeing: * For v4, some of our IOS routers are agreeing on 1,440 bytes, while others on 8,916 bytes. Need to look into the difference here - I recall we recently replaced a defective route reflector, which is the one registering the higher MTU. * For v6, all our IOS routers are agreeing on 8,896 bytes. Interface MTU is 9,000 bytes on all router interfaces. IOS code is 12.2(33)SRC3. We have nearly similar values for our JunOS routers peering with the route reflectors, but not sure that's relevant here. Suffice it to say that 'ip tcp path-mtu-discovery' isn't configured, although it is enabled by default for BGP: #sh ip bgp neighbors <snip> Transport(tcp) path-mtu-discovery is enabled #sh bgp ipv6 unicast neighbors <snip> Transport(tcp) path-mtu-discovery is enabled For routers where we've configured 'no bgp transport path- mtu-discovery' under the BGP process (for troubleshooting/testing), we've registered an agreed value of 516 bytes. eBGP sessions to downstreams is at 1,440 bytes. Cheers, Mark.
signature.asc
Description: This is a digitally signed message part.
_______________________________________________ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/